Mean (± S.E.) change from baseline in the 6-min walk distance for bosentan (n = 21) and placebo (n = 11) groups. Mean (± S.E.) change from baseline in the 6-min walk distance for bosentan (n = 21) and placebo (n = 11) groups. Patients who did not complete week 20 assessments (bosentan, n = 1; placebo, n = 4) had their last observed values carried forward. *, P < 0.05 versus baseline, P = 0.021 versus placebo at week 12. [Reprinted from Channick RN, Simonneau G, Sitbon O, Robbins IM, Frost A, Tapson VF, Badesch DB, Roux S, Rainisio M, Bodin F, et al. (2001) Effects of the dual endothelin-receptor antagonist bosentan in patients with pulmonary hypertension: a randomised placebo-controlled study. Lancet358:1119–1123. Copyright © 2001 Elsevier, Inc. Used with permission.] Lyn R. Frumkin Pharmacol Rev 2012;64:583-620 © 2012 by The American Society for Pharmacology and Experimental Therapeutics